1. Field of the Invention
The present invention is directed to a signalling transmission system for transmitting and receiving voice and signalling signals via, for example, a telephone line.
2. Description of the Prior Art
Turning first to FIG. 1, a block diagram of a conventional signalling transmission system is illustrated.
In FIG. 1, the reference numeral 1 denotes an encoding module which incorporates a voice encoder, generally indicated at 2, for encoding voice signals into 320 bits/frame at a bit rate of 16 kbps, namely 20 msec/frame, and a signalling encoder, generally denoted as 3, for encoding signalling signals by sampling it at a frequency of 800 Hz. The numeral 4 represents an input signal line for inputting the voice signals; 5 an input signal line for inputting the signalling signals; 6 an output signal line, dedicated to transmission at the bit rate of 16 kbps for outputting the voice signals encoded by the voice encoder 2; and 7 an output signal line, dedicated to transmission at a bit rate of 800 bps for outputting the signalling signals encoded by the signalling encoder 3.
The numeral 10 designates a decoding module which incorporates a voice decoder, generally identified as 11, for decoding the encoded voice signals of 16 kbps into the original voice signals, and a signalling decoder, generally denoted as 12, for decoding the encoded signal signals of 800 bps into the original signalling signals. The numeral 13 denotes an input signal line for inputting the voice signals which have the bit rate of b 16 kbps to the voice decoder 11; 14 an input signal line for inputting the signalling signals which dedicates the bit rate of 800 bps to the signalling decoder 12; 15 an output signal line for outputting the voice signals decoded by the voice decoder 11; 16 an output signal line connected with the signalling decoder 12; 20 a channel transmission path through which the voice signals of 16 kbps are transmitted from the output signal line 6 to the input signal line 13; and 21 a channel transmission path through which the signalling signals of 800 bps are transmitted from the output signal line 7 to the input signal line 14.
Under such an arrangement, encoding module 1 may be regarded as a transmitting module, whereas the decoding module 10 may be defined as a receiving module.
The description will next deal with the function of the system.
When the voice signals are input via the input signal line 4 to the voice encoder 2, the voice encoder 2 encodes the voice signals into 320 bits/frame with 20 msec/frame and transmits these signals encoded at 16 kbps to the output signal line 6. A synchronization signal consisted of 4 bits is incorporated in the top of the frame.
When the signalling signals are received through the input signal line 5, the signalling encoder 3 operates to encode these signalling signals by sampling it at a frequency of 800 Hz and transmitting the signals encoded at 800 bps on the output signal line 7.
The voice and signalling signals on the output signal lines 6 and 7 are transmitted to the decoding module 10 through the voice signal channel transmission path 20 dedicated to 16 kbps transmission and the signalling signal transmission path 21 dedicated to 800 bps transmission, respectively.
On the receiving side, the voice and signalling signals transmitted via the respective channel transmission paths 20 and 21 are decoded by means of the voice decoder 11 and signalling decoder 12, and are then output therefrom. FIG. 2 illustrates a transmission form for a voice group, while FIG. 3 depicts a transmission form for a signalling group. Note that the numerals shown in FIGS. 2 and 3 correspond to those with which the blocks and signal lines are marked in FIG. 1.
The encoded voice signals and the encoded signalling signals may be transmitted via physically separated digital transmission paths 20 and 21 as indicated in FIG. 1, or also may be transmitted via time-division-multiplexed one digital transmission line occupying transmission channel capacity of 16.8 kbps.
The prior art signalling transmission system is, as discussed above, adapted to transmit and receive the signalling signals separately from the voice signals via the individual transmission channel, and is therefore associated with a problem of decreasing transmission efficiency.